The healthy heart produces regular, synchronized contractions. Rhythmic contractions of the heart are normally controlled by the sinoatrial (SA) node, specialized cells located in the upper right atrium. The SA node is the normal pacemaker of the heart, typically initiating 60-100 heart beats per minute. When the SA node is pacing the heart normally, the heart is said to be in normal sinus rhythm (NSR).
Bradycardia occurs when the heart rhythm is too slow. This condition may be caused, for example, by delayed impulses from the SA node, denoted sick sinus syndrome, or by a blockage of the electrical impulse between the atria and ventricles. Bradycardia produces a heart rate that is too slow to maintain adequate circulation.
Implantable cardiac rhythm management systems, such as pacemakers, have been used as an effective treatment for patients with bradycardia. These systems typically comprise circuitry to sense signals from the heart and a pulse generator for providing electrical pulses to the heart. Leads extending into the patient's heart are connected to electrodes that contact the myocardium for sensing the heart's electrical signals and for delivering pulses to the heart in accordance with various pacing therapies.
Pacemakers deliver low energy electrical pulses timed to assist the heart in producing a contractile rhythm that maintains cardiac pumping efficiency. Pace pulses may be intermittent or continuous, depending on the needs of the patient. There exist a number of categories of pacemaker devices, with various modes for sensing and pacing the heart. Single chamber pacemakers may pace and sense one heart chamber. A typical single chamber pacemaker is connected to a lead extending either to the right atrium or the right ventricle. Dual chamber pacemakers may pace and sense two chambers of the heart. A typical dual chamber pacemaker is typically connected to two leads, one lead extending to the right atrium and one lead to the right ventricle. Biventricular pacemakers may be used to provide pacing pulses to both the left ventricle and the right ventricle. Biventricular pacing may be particularly advantageous for delivering cardiac resynchronization therapy for patient's suffering from congestive heart failure (CHF).
If a pace pulse produces a contraction or “captures” the heart tissue, an electrical signal associated with the contraction may be detected and used to confirm that capture has occurred. Pace pulses that fail to produce a contraction in the heart tissue result in non-capture. Non-capture may occur when the pacing pulse energy is too low, and/or if the pacing pulse is delivered during a refractory period of the cardiac tissue.
The present invention involves enhanced methods and systems for verifying capture and provides various advantages over the prior art.